dataroom/lib/utils/determine-text-color.ts

function hexToRgb(hex: string) {
  let r = 0,
    g = 0,
    b = 0;
  // 3 digits
  if (hex.length === 4) {
    r = parseInt(hex[1] + hex[1], 16);
    g = parseInt(hex[2] + hex[2], 16);
    b = parseInt(hex[3] + hex[3], 16);
  }
  // 6 digits
  else if (hex.length === 7) {
    r = parseInt(hex[1] + hex[2], 16);
    g = parseInt(hex[3] + hex[4], 16);
    b = parseInt(hex[5] + hex[6], 16);
  }
  return [r, g, b];
}

function luminance(r: number, g: number, b: number) {
  return (0.299 * r + 0.587 * g + 0.114 * b) / 255;
}

export function determineTextColor(hexColor: string | null | undefined) {
  if (!hexColor) return "white";
  const [r, g, b] = hexToRgb(hexColor);
  return luminance(r, g, b) > 0.5 ? "black" : "white";
}